Lupus is a chronic auto-immune disease with symptoms that include body aches, fevers and extreme fatigue. It can also lead to kidney and heart damage.

"I'm very aware some of my fans had noticed I was laying low for part of the summer and questioning why I wasn't promoting my new music, which I was extremely proud of," Gomez wrote.

"So I found out I needed to get a kidney transplant due to my Lupus and was recovering. It was what I needed to do for my overall health.

"I honestly look forward to sharing with you, soon my journey through these past several months as I have always wanted to do with you.

"Until then I want to publicly thank my family and incredible team of doctors for everything they have done for me prior to and post-surgery."

Selena Gomez has revealed she's had a kidney transplantSource:Instagram

Gomez, who is dating singer The Weekend, went on thank The Secret Life of the American Teenager star Raisa who had donated her kidney, revealing she felt "incredibly blessed".

Raisa and Gomez have been friends for more than eight years and even call each other sisters.

"And finally, there aren't words to describe how I can possibly thank my beautiful friend Francia Raisa," she wrote.

She gave me the ultimate gift and sacrifice by donating her kidney to me. I am incredibly blessed. I love you so much sis."

And helping to raise some awareness about Lupus, she added: "Lupus continues to be very misunderstood but progress is being made. For more information regarding Lupus please go to the Lupus Research Alliance website: www.lupusresearch.org"

Last year Raisa paid tribute to her BFF on her birthday, revealing she had been there for her through thick and thin.

She wrote: "There are so many moments we have and things you do that I cherish and don't take for granted. Whether it's crying, laughing, or simply sitting on my kitchen floor throwing our hands up in the air confused at life, I'm thankful you're always there."

She added: "It's been so inspiring watching you grow and to grow with you. I learn so much from you and I'm so so so proud of you."

Gomez first opened up about having Lupus in 2015 and last year she was forced to take a break from the limelight after suffering from anxiety, panic attacks and depression - stemming from the disease.

She told fans at the time: "As many of you know, around a year ago I revealed that I have lupus, an illness that can affect people in different ways.

"I've discovered that anxiety, panic attacks and depression can be side-effects of lupus, which can present their own challenges.

"I want to be proactive and focus on maintaining my health and happiness and have decided that the best way forward is to take some time off."

After opening up about her Lupus she admitted the support had been 'overwhelming' and revealed why she had waited to speak about it publicly.

She told Billboard: "It has been overwhelming and the response has been very supportive, which is nice - but it still makes me a little uncomfortable.

"I waited for the right time to talk about it because I am in a great place and I'm very healthy. I'm not trying to be loud about it: It was time to use my platform to help."